The subject matter disclosed herein relates to a flexible command model that provides for aircraft control and, more particularly, to a flexible command model for amplitude-based mode blending that provides for aircraft control.
In aircraft and, more particularly, in rotorcraft and helicopter control systems, fly-by-wire (FBW) model-following control laws allow for the specification of a command model that determines the relationship between a pilot's stick input and the aircraft response, which is typically defined in terms of an angular rate or a linear velocity. As such, the selection of the command model can have a dramatic effect on the handling qualities of the aircraft. Indeed, the choice and the parameterizations of the command model response type involve tradeoffs of aircraft maneuverability versus aircraft stability.
Command model response types generally include rate command, attitude command and translational rate command models. In rate command attitude hold (RCAH) response type models, the pilot's stick deflection is proportional to a quasi-static angular rate response of the aircraft and when no rate is commanded the aircraft attitude is held steady. In attitude command velocity hold (ACVH) response type models, the pilot's stick deflection is proportional to a quasi-static angular attitude response of the aircraft and when no attitude is commanded the velocity is held steady. RCAH command modes can thus be viewed as a more maneuverable response type while ACVH command modes can thus be viewed as a more stable response types. Of course, other response types, such as translational rate command response types, may also be employed.
Existing FBW aircraft can, in some cases, utilize multiple pilot selectable response types but such cases involve software complexity, test cost increases and potential pilot confusion. Alternatively, FBW aircraft can utilize a single response type and compromise on either stability or maneuverability. In particular cases, a notion of frequency splitting of the pilot stick command was explored in order to combine the characteristics of multiple response types in a single mode that would then achieve some measure of maneuverability and stability.